Finally，many people believe that perfect signal balance is required to reject noise in balanced interfaces. While signal balance helps maintain headroom， it does not affect the common-mode rejection of the source/receiver system (impedance balance and CMR is what counts to reject hum and noise).
Especially in discrete balanced output stages, some designers trim signal balance by using a pot connected between the two outputs with its wiper grounded. (See Figure 2 .) But，the best CMR of the source/receiver system occurs at a very different setting from that which achieves best signal balance. Of course， this concern can be largely eliminated by turning to the popular integrated solutions， which guarantee high common-mode rejection through careful trimming of the internal resistors.
Balanced Output Stage With Bridged Feedback
In balanced signal transmission, two identical signals are transmitted simultaneously with inverted phase and combined at the receiving end, thereby canceling out common-mode noise and interference. This assures pure high-quality signal transmission. The principle of balanced sound transmission is shown in Figure 4. The outputs of the two amplifiers AMP1 and AMP2 are connected to form a cross-feedback loop, which sends the symmetrical (+) and (-) signals with low impedance to the next stage. The signals are isolated from the ground line, resulting in an ideal balanced circuit. Even if one side of the output is grounded, both amplifiers continue to operate, and the output voltage does not change.
发表于 2022-7-17 07:47
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